Frequency converter



FIG. 1 is a top, front, right perspective view of a frequency converter, showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines of even length shown in the drawings illustrate portions of the frequency converter that form no part of the claimed design. 

CLAIM The ornamental design for a frequency converter, as shown and described. 